Characteristics and causes of variation of karst groundwater level in the Niangziguan spring area

The Niangziguan spring is one of the largest karst springs in north China.Its clusters are exposed in the Niangziguan town,Pingding county,Yangquan City,Shanxi, with an average annual discharge of 9.81m3s-1and catchment area about 7435.8 km2. This spring is the most important water supply source of Yangquan City,which plays an irreplaceable support in urban life and industrial and agricultural production and construction.Under the background of climate change and the increasing intensity of human activities,it is facing some challenging problems,such as the decline of spring flow,water pollution and the continuous decline of karst groundwater level. To further address this issue,based on variation monitoring data of many years, combined with the conditions of groundwater recharge, runoff and drainage,this paper analyzes the characteristics and causes of dynamic changes of karst groundwater in this area.The results show that,(1)overall the water flow declined from 1980 to 2004,then tended to be stable and slightly recovered after 2004;(2)The spatial variation of the groundwater recharge area is larger than that of the runoff area. The variation in time is divided into two stages:1980-2004 and 2005-2014.In the first stage,the water level showed a continuous decline trend,while in the second stage it experienced a slow decline with fluctuations and small rise at local places.From January 1998 to January 2004,the karst groundwater level in Longzhuang decreased by 22.9 meters,with an average annual variation of 3.82 m.From May 2005 to May 2014, it increased by 1.5 meters with average annual change -0.17 m.